The proposed studies are designed to develop and standardize a radioimmunoassay (RIA) system for the identification of hemoglobin variants and for the prenatal diagnosis of hemoglobinopathies. The system unequivocally distinguishes hemoglobins with single amino acid differences. It is expected further to yield information on the general location of the amino acid substitution in variant hemoglobins, and to sense a number of internal modifications of hemoglobin not ordinarily available to immunological detection. The prenatal diagnosis of hemoglobinopathies utilizes the RIA system. A prerequisite of this application is the isolation of fetal red cells free of contamination with maternal blood; experiments for developing an appropriate technique are proposed.